A battery may comprise one or more individual cells. Typically, a single electrochemical cell is composed of a negative electrode (anode) and a positive electrode (cathode) separated by an electrolytic solution. When the cell is discharging, the chemical energy is converted to electrical energy. Initially, batteries are assembled with high energy chemical compounds, and the stored chemical energy is withdrawn as electrical energy at some later time. Primary batteries are batteries that sold in their charged state and discarded without recharge. When primary batteries are completely discharged, they are discarded.
Secondary batteries, on comparison, belong to a different category of batteries from the primary batteries, in that the secondary batteries can discharge their energy and be recharged. The chemical, electrochemical, and physical properties associated with both types of batteries are the same, the main difference being the nature of the electrochemically active material used in the system. Recharging in secondary batteries is accomplished by forcing an external current through the battery in a direction opposite to the current flow during discharge so as to restore the electrochemically active material to their original charged condition. A secondary battery can discharge and be recharged as many as several thousand times depending on the use and operating condition. This is the chief advantage of the secondary battery relative to the primary battery; however, a secondary battery typically provides lower energy density and high initial cost.
More recently, primary lithium batteries have been widely used in portable electronic products, and have maintained a stable market share. On the other hand, the commercialization of secondary lithium batteries has been relatively slow in coming. The main problem associated with secondary lithium batteries discouraging their market acceptance, is the formation of lithium dendrites during the recharging process. The lithium dendrites so formed can puncture through the partition membrane separating the anode and the cathode; this causes short circuiting and thus raising serious safety concerns. To improve the safety of using secondary lithium batteries, other metals have been researched to replace lithium as the anode material. One of the more commonly employed approaches is to use lithium alloy as anode material in a lithium ion system. An example is to use to Li-Al alloy as the primary anode material in a secondary lithium battery. A good anode material should provide good capacity for the intercalation and deintercalation of the lithium ions. Carbon powders have been known to provide a good base material for use as anode.
U.S. Pat. No. 4,985,317, the content thereof in incorporated herein by reference, discloses a lithium ion-conductive solid electrolyte consisting of a compound represented by the chemical formula of Li.sub.1+x M.sub.x Ti.sub.2-x (PO.sub.4).sub.3, wherein M can be Fe or Al, a compound represent by the chemical formula of Li.sub.1+y Ti.sub.2 Si.sub.y P.sub.3-y O.sub.12, or a compound obtained by mixing a compound represented by the chemical formula of LiTi.sub.2 (PO.sub.4).sub.3 and any other lithium compound. However, the '317 does not address the issue of providing an improved anode material for use in secondary lithium batteries. Japanese Laid Open Patent Applications JP3-81908 and JP3-29206 also disclosed the use of titanium phosphate electrolytes; however, they also did not address the issue of providing an improved anode material for use in secondary lithium batteries.